This invention relates to tool components and more particularly to cutting components for drill bits.
Abrasive compacts are well known in the art and are used for a variety of abrading operations such as cutting, drilling, grinding and the like. Abrasive compacts consist of a polycrystalline mass of bonded abrasive particles, the abrasive particle content of which is at least 70 percent by volume and generally 80 to 90 percent by volume. The abrasive particles may be self-bonded without the aid or use of a second or bonding phase. Alternatively, a second or bonding phase may be provided. The abrasive particles for compacts are invariably diamond or cubic boron nitride.
Abrasive compacts may be bonded to cemented carbide supports. Such bonded compacts are often referred to as composite compacts. Bonding between the compact and the carbide support may be direct but without the interposition of a braze layer. Alternatively, a bonding braze layer may be provided between the compact and the carbide support.
A more detailed description of abrasive compacts and composite compacts may be found in a number of published patent specifications, for example U.S. Pat. Nos. 3,743,489, 3,767,371, 4,063,909 and 3,745,623.
Rotary drills used for oil and gas well drilling and core drilling generally comprise a drill bit having formed thereon a plurality of preformed sockets in which cutting elements or components are mounted. The cutting elements or components may be brazed, force fitted or heat shrunk into the sockets. Typical cutting elements used in the prior art are steel teeth, steel teeth laminated with tungsten carbide, inserts of cemented tungsten carbide and natural diamonds.
Cutting components for drill bits and utilising composite compacts have also been described in the literature and have been used commercially. Such cutting elements comprise an elongate pin of cemented carbide to which is bonded a composite compact, bonding being achieved through the carbide support of the composite compact. Bonding between the carbide support and the elongate pin is achieved by a braze metal which has a melting point above 700.degree. C. Such a high temperature braze, so the art teaches, is essential in order to achieve a sufficiently strong bond between the composite compact and the elongate pin. Reference in this regard may be had to the disclosures of U.S. Pat. No. 4,225,322.
It has also been proposed to produce a cutting component utilising composite compacts by forming a pocket or recess in an elongate pin to accommodate the composite compact. The composite compact is located in the pocket or recess and then brazed thereto using a braze such as Easy Flo 45 braze. Reference in this regard may be had to the article "Design, Fabrication and Field Test Performance of Slug-type Diamond Compacts Oil Bits" by W. H. Daniels and D. A. Thompson, Journal of Energy Resources Technology, March 1979, Vol. 101 pages 41 to 45. To the best of the Applicant's knowledge, such cutting components have never been used commercially. It is believed that one of the reasons why such cutting components have not been used commercially is that a stress concentration caused by the pocket apparently makes the carbide mounting pin a weaker link. Fracture of the pin through the pocket zone occurs.